As a data transmission system for transmitting data in a vehicle, there is a known system in which an optical fiber cable is disposed in the vehicle, and non-time-series data such as a command and time-series data such as video data are transmitted using the optical fiber cable.
In the data transmission system, there is a synchronous ring type network for the purpose of transmitting time-series audio data, video data and the like. In the synchronous ring type network, as shown in FIG. 1, communication devices each comprising a master device and slave devices are connected to one another in a ring-like form, and data is transmitted in synchronization with data transmission timing between the communication devices.
In such a synchronous ring type network, as shown in FIG. 2 for example, electronic equipments A, B and C are disposed in a front portion of a vehicle near a front seat, and electronic equipments D and E are disposed near a rear seat. The electronic equipments are connected to one another in a ring-like form through optical communication lines 101 comprising optical fiber, and transmit data while relaying an optical signal in a predetermined direction. A power source line 102 is disposed in this synchronous ring type network. The power source line 102 comprises electric wire for supplying power source to each electronic equipment. The power source line 102 has a wire harness separately from the optical communication line 101. The reason why the optical communication line 101 and the power source line 102 utilize the different wire harnesses is that the optical communication lines 101 are connected in a ring-like form but the power source line 102 is branched off at each electronic equipment to which power source is supplied.
According to the synchronous ring type network, when all the electronic equipments are actuated and communication is started, it is necessary to carry out a wake-up processing for individually actuating the electronic equipments. However, in the conventional synchronous ring type network, photoelectric converters (FOT) provided in the electronic equipments are brought into standby states, and optical signal is sent to the slave devices A, B and C from the master device in this order, thereby waking them up. Thus, dark current (standby current) for bringing the electronic equipments in standby states is generated.